QUESTIONS AND ANSWERS 137 



State the function of the corpora nigra (pigmentary bodies of the iris). 

 Assist in absorbing rays of light. 



Describe the process of focal accommodation. 



The crystalline lens becomes more convex for near objects be- 

 cause the rays are more divergent. This convexity is brought about 

 by the bulging of the lens when the tension on the capsule is lessened 

 by the action of the ciliary muscle which contracts and draws for- 

 ward the choroid coat and with it the ciliary processes. A reversal 

 of this process will produce a lesser convexity of the lens and thus 

 properly focus distant objects. 



What are the functions of the lachrymal secretion? 



It lubricates the conjunctiva, keeps the cornea brilliantly polished 

 and washes away foreign bodies. 



Describe fully the function of the auditory nerve. 



Special sense of hearing and through its connection with the 

 semicircular canals assists in maintaining the equilibrium of the 

 body. 



How do the auditory sensations reach the brain? 



The tympanum receives the sound wave and transmits it through 

 the chain of bones (malleus, incus and stapes) to the fenestra ovalis 

 which imparts an impidse to the perilymph of the labyrinth; the 

 perilymph carries the impulse through the vestibule and from 

 here it is carried into the scala vestibuli of the cochlea. The vibra- 

 tions pass through the spiral-shaped cochlea and set in motion the 

 membrane of Reissner ; this causes the lymph in the cochlear canal 

 to vibrate and reach the scala tympani. The lymph in this canal 

 is now set in motion and affects the basilar membrane on which 

 the organ of Corti rests. The auditory nerve ends in the organ of 

 Corti, so the impressions are carried from this organ to the brain. 



What is the function of the Eustachian tube? 



It allows an equalization of pressure on both sides of the mem- 

 brani tympani. 



Name the four primary taste sensations. 

 Sweet, bitter, acid and salt. 



What nerves are concerned in the sensation of taste? 



The gustatory branch of the fifth pair of cranial nerves, which 

 receives fibres from the chorda tympani of the seventh pair, sup- 

 plies the taste buds on the anterior two-thirds of the tongue. The 

 posterior one-third is supplied by the glossopharyngeal. 



